The invention relates to an oil pump, and more particularly, to an oil pump, the pumping action of which can be turned on and off as required.
An oil pump of vane type generally comprises a cam ring having a substantially elliptical cam surface around its inner periphery, a rotor disposed for rotation inside the cam ring, a plurality of vanes fitted in the rotor for reciprocating motion in their associated radially extending slits, and a pair of pressure plate and side plate which act to hold the rotor and the cam therebetween from the opposite sides. As the rotor rotates, the volume of a pump chamber defined between a pair of adjacent vanes increases and decreases, thus serving the suction and discharge of oil. In order to achieve a reliable sliding contact of the vane tip with the cam, a groove is formed in the pressure plate to introduce oil which is discharged from the pump chamber so as to act against the back side of the vane.
When the described oil pump is mounted on a vehicle, the pumping action must be turned on and off as desired. In the prior art practice, the turn-on and-off of the pumping action has been achieved by means of a clutch were the pump is driven from an associated engine through a belt, or by turning an electric motor on and off where the pump is driven by such motor. However, the prior art arrangement incorporating such clutch or motor is bulky and is also disadvantageous in respects of control, reliability and costs.